While former Boston Mayor Thomas Menino is upbeat and seemingly confident about his future after a diagnosis of an advanced form of cancer that has spread to his liver and lymph nodes, medical experts said Menino has a difficult fight ahead.

"When it spreads to the liver, we typically would say it is not curable, but based on how well people do with chemotherapy is really is how well they are going to do," said Dr. David Ryan, chief of hematology at Massachusetts General Hospital, who is not treating the former mayor.

Menino, 71, began to undergo the cancer treatment in early March at Dana-Farber Cancer Institute.

Dot Joyce, Menino's spokeswoman, calls him "one tough cookie."

"At an event in Dorchester Sunday afternoon for the children's book "Goodbye, Mayor Menino," the former mayor told reporters that he's a "fighter."

"I'm not going to sit in my house and read books and watch television," Menino said. "I'm going to go to my office tomorrow morning at 9 o'clock and do my work."

Menino added that he doesn't feel sorry for himself and said he feels lucky to live in Boston, which he called a "family city."

"When something happens to somebody else, we all rally. Look what happened after the marathon bombings, how we rallied them," Menino said. "People are calling me wishing me good luck. Who am I? I'm just a guy from Hyde Park."

The cancer that had metastasized is said to have no connection to Menino's series of medical problems in his last years as mayor, his doctors said.

In 2003, he underwent surgery to remove a rare sarcoma on his back. The following year, his doctors confirmed he has been diagnosed with Crohn's disease, a type of inflammatory bowel disease.

He spent six weeks in the hospital in 2012 for a series of ailments, including a respiratory infection. While he was in the hospital, he suffered a compression fracture in his spine and was diagnosed with Type 2 diabetes.

In May 2013, he was back in the hospital for surgery for an enlarged prostate.

Boston Mayor Marty Walsh said at Sunday's St. Patrick's Day Breakfast in Boston that he spoke to Menino on Saturday night, and the former mayor told him that he'd "beaten this before."

"Mayor Menino was a great mayor for the City of Boston for the past 20 years," Walsh said. "He's left a great legacy and I want to wish him a speedy recovery."